Regular antenna systems are challenged by:
High-rise building coverage: Limited directive antennas (in azimuth/elevation plan) resulting on limitation in terms of high order sectorization.
Capacity lift at Macro Site and Uplink Coverage& Capacity Limited: for a given allocated time-frequency, there is still a challenge during multiplexing of different users due to small number of available antennas being able to direct azimuth narrow beam at desired direction while nulling interferers of intra- and inter-cell efficiently. Besides, business expansion along with difficulty in acquiring new site where UL: DL is 1:3.
High In-Building Capacity growth: even in claimed SU-MIMO, resources are not exploited fully due to limited size of user devices. Besides, higher cost for in-building system, with poor WLAN performance.
Massive MIMO antennas have been recently investigated to tackle the above challenges and being Key technology driving 4.5G and beyond. Spectrum efficiency is increased by smart collocated or conformal antenna arrays along with vertical beam adjustment. In one word, 3D MIMO with standards is being promoted with effort, prototype along with network deployment pilot. In the Long-term, beam forming in higher frequency and hardware progress will be considered.
In traditional Massive MIMO antennas, a cavity backed filter is generally used at the back of the antenna with number of outputs same as the number of antenna ports. And the inputs of the filter are connected to a number of Transmitting/Receiving circuits (from RRU). Besides costly development and implementation resources, drawbacks such as weight, size and integration flexibility issues as different hardware have to be designed separately prior to integrating.